[1][2] Hamza Bey first appeared in 1421, when his brother, Bayezid Pasha, tried unsuccessfully to stop Mustafa Çelebi from taking Edirne.
Hamza Bey came to prominence, as a commander in Murad II's fleet, during the siege of Thessalonica, which in 1430 was ultimately successful.
In the final assault on the city, in order to prevent defenders from the reinforcing the critical northern and western parts of the wall, Hamza and the Ottoman fleet was to provide diversionary attacks against the sea walls of Constantinople in the south, on the Sea of Marmara; and against the dam across Golden Horn in the east.
However, stalled by the Knights of Rhodes, Hamza was unable to take the remainder of the Aegean, leaving Christian forces astride the Ottoman route from their new capital to the Mediterranean proper.
[5][6] According to Laonikos Chalkokondyles, upon hearing this, Mehmed lost his temper and became angered, so much so that he struck Mahmud Pasha, who brought the news.